1. Field of the Invention
The present invention relates generally to a semiconductor process, and more specifically to a semiconductor process applying thermal treatments on metal gates.
2. Description of the Prior Art
Field effect transistors are important electronic devices in the fabrication of integrated circuits, and as the size of the semiconductor device becomes smaller and smaller, the fabrication of the transistors also improves and is constantly enhanced for fabricating transistors with smaller sizes and higher quality.
Poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as transistors. With the trend towards scaling down the size of semiconductor devices, however, conventional poly-silicon gates face problems such as inferior performance due to boron penetration and unavoidable depletion effect. This increases equivalent thickness of the gate dielectric layer, reduces gate capacitance, and worsens a driving force of the devices. Therefore, work function metals that are suitable for use as the high-K gate dielectric layer are used to replace the conventional poly-silicon gate to be the control electrode.
Moreover, with a trend towards scaling down the size of transistors, the thickness of agate dielectric layer must be reduced; if the gate dielectric layer is insufficient for sustaining a breakdown voltage, however, the phenomenon of serious leakage current will occur. Hence, processes may be necessary to improve the quality of the gate dielectric layer. How to establish processes suitable for improving the quality and the reliability of high-k dielectric layer is therefore an important issue in the field.